Cryotreatment devices and methods of forming conduction blocks

ABSTRACT

Cryotreatment devices and methods of ablating tissue within the body are disclosed. A cryotreatment device in accordance with an exemplary embodiment of the present invention includes an elongated member having one or more needle-like ablation tips configured to induce necrosis at a target site within the heart. A cooling fluid such as a cryogen may be injected through a lumen extending into the distal portion of the device. The ablation tips can be configured to pierce and ablate surrounding tissue, blocking electrical stimuli that can cause fibrillations or other arrhythmias of the heart. The device may also include means for controlling the transmural depth at which the ablation tips are inserted into the cardiac tissue. Methods of forming a contiguous line of conduction block in accordance with the present invention are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. application Ser.No. 12/485,697, filed Jun. 16, 2009; which is a divisional of and claimspriority to U.S. application Ser. No. 10/411,601, filed Apr. 10, 2003,now abandoned, the entire disclosures of which are all incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates generally to medical devices for ablatingtissue at one or more target sites. More specifically, the presentinvention relates to cryotreatment devices and methods for inducingcontrolled necrosis of cardiac tissue within the heart.

BACKGROUND OF THE INVENTION

Cardiac arrhythmias such as atrial fibrillation, bradycardia,ventricular tachycardia, ventricle fibrillation, andWolff-Parkinson-White syndrome are common heart abnormalities that causestroke, myocardial infarction, and other thromboembolic events withinthe body. In patients with normal sinus rhythm, the heart iselectrically excited to beat in a synchronous and patterned manner,typically at a rate of 60 to 100 beats per minute (bpm). In contrast, inpatients with cardiac arrhythmia, abnormal regions of the cardiac tissuemay aberrantly conduct to adjacent tissue, causing the heart to beatirregularly. In ventricular tachycardia, for example, electrical signalsmay be errantly received in the lower heart chamber (i.e. the ventricle)instead of the right, upper chamber (i.e. the atria), causing the heartto beat rapidly. In atrial fibrillation, the most common type of cardiacarrhythmia, the upper chambers of the heart beat at an uncontrolled rateof 350 to 600 bpm, which results in a reduction of the pumping force ofthe heart. As a result of this reduced pumping force, blood in the heartchambers may become stagnant and pool, forming blood clots that candislodge within the body and cause stroke or other life threateningevents.

To treat cardiac arrhythmia, a number of therapeutic procedures havebeen developed, including RF catheter ablation, chemical cardioversion,percutaneous myocardial revascularization (PMR), and suppression.Antiarrhythmic medications such as beta-blockers, calcium channelblockers, anticoagulants, and DIGOXIN have also been used successfullyto treat some forms of cardiac arrhythmia. More recent trends havefocused on the use of cryotreatment catheters to treat arrhythmias suchas atrial fibrillation and ventricular tachycardia. Such devices providea relatively non-invasive method of treatment in comparison to othersurgical techniques.

In one such method, for example, a catheter loaded with a cryogeniccooling fluid may used to cryogenically cool cardiac tissue at strategiclocations of the heart, such as the right and left atria, or thepulmonary veins. The catheter can be used to induce necrosis at one ormore pre-mapped target sites within the heart to create conductionblocks within the aberrant electrical conduction pathways. In atrialfibrillation, for example, necrosis of one or more target sites withinthe atrial cardiac muscle tissue can be used to block the electricalsignals believed to cause and/or sustain the fibrillation.

In some techniques, the use of a cryotreatment device to form therequired conduction block may be ineffective since there is no adequatemeans to control the transmural depth of the lesion, or the distancebetween each lesion. To compensate for these shortcomings, manycryotreatment devices utilize relatively large catheter tips, whichdestroy more tissue than is necessary to form the conduction block andfurther reduce the already weakened pumping force of the heart. It istherefore desirable to have a cryotreatment device capable oftransmurally controlling the depth of each lesion and in a contiguousmanner.

SUMMARY OF THE INVENTION

The present invention relates generally to cryotreatment devices andmethods for reducing or eliminating arrhythmia by inducing controllednecrosis at one or more pre-mapped target sites within the heart. Acryotreatment device in accordance with an exemplary embodiment of thepresent invention may comprise an elongated member having a proximalportion, a distal portion, and one or more lumens therein in fluidcommunication with a cooling fluid adapted to cool the distal portion ofthe elongated member. The elongated member may include one or moreneedle-like ablation tips configured to pierce and necrotize cardiactissue within the heart, preventing the conduction of aberrantelectrical signals through the tissue to one or more relay sites ofarrthymogenic foci. The cryotreatment device may include one or morefeatures configured to form an array of ablations within the cardiactissue, forming a contiguous line of conduction block.

The ablation tips may be retractable within the elongated member tocontrol the penetration depth of the tips transmurally into the cardiactissue. A pull cord operatively coupled to the ablation tip can be usedto retract the ablation tip from the cardiac tissue. An ultrasonic probeor other measuring device may also be provided to measure and controlthe insertion depth of the cryotreatment device within the cardiactissue.

A cryosurgical method in accordance with the present invention maycomprise the steps of providing a cryotreatment device to a target sitewithin the heart, and necrotizing one or more locations within thecardiac tissue to form a contiguous line of conduction block. A coolingfluid such as liquid nitrous oxide can be injected through an innerlumen extending to the distal portion of the cryotreatment device tocool the surrounding tissue adjacent the ablation tips.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a cryotreatment device in accordance withan exemplary embodiment of the present invention, wherein the device isshown inserted through the septal wall of the heart and advanced to atarget site at or near one or more relay points;

FIG. 2 is a partial cross-sectional view of the cryotreatment device ofFIG. 1;

FIG. 3 is a detailed view of the cryotreatment device of FIGS. 1-2,wherein the device includes an ultrasonic probe adapted measure andcontrol the transmural depth of the device into the cardiac tissue;

FIG. 4 is another detailed view illustrating multiple cryotreatmentdevices coupled together using a coupling member;

FIG. 5 is a view of a cryotreatment device in accordance with anexemplary embodiment of the present invention, wherein the cryotreatmentdevice includes a linear array of ablation tips;

FIG. 6 is a partial cross-sectional view of a cryotreatment device inaccordance with an exemplary embodiment of the present invention,wherein the cryotreatment device includes several retractable cryogenictips configured to form a circumferential line of conduction blockwithin the heart; and

FIG. 7 is a partial cross-sectional view of a cryotreatment device inaccordance with another exemplary embodiment of the present invention,wherein the cryotreatment devices includes an enlarged distal portionwith retractable ablation tips.

DETAILED DESCRIPTION OF THE INVENTION

The following description should be read with reference to the drawings,in which like elements in different drawings are numbered in likefashion. The drawings, which are not necessarily to scale, depictselected embodiments and are not intended to limit the scope of theinvention. Although examples of construction, dimensions, and materialsare illustrated for the various elements, those skilled in the art willrecognize that many of the examples provided have suitable alternativesthat may be utilized.

FIG. 1 is an illustrative view of a cryotreatment device 10 inaccordance with an exemplary embodiment of the present invention forinducing controlled necrosis at one or more pre-mapped target siteswithin the heart. A guide wire 12 inserted percutaneously into thefemoral or jugular veins is shown advanced through the septal wall 14and into the upper chambers 16,18 of a heart 20. Using knownmanipulation techniques in the art, guidewire 12 can be advanced to alocation distal a target site 22 determined to cause electricalinterference with one or more downstream arrythmogenic foci 24. A guidecatheter 26 sufficiently sized to receive cryotreatment device 10 can beused to advance the cryotreatment device 10 to a location at or near thetarget site 22.

Arrhythmias such as atrial flutter, atrial fibrillation and ventriculartachycardia are typically caused when abnormal regions of the hearttransmit aberrant electrical signals vis-a-vis arrythmogenic foci. Totreat such arrhythmias, a cryotreatment device in accordance with thepresent invention can be inserted into cardiac tissue at a pre-mappedtarget site and cooled to a temperature of about −40 to −100° C. toinduce necrosis at one or more locations 28,30,32,34 within the heart,such as the pulmonary vein 36. The cryotreatment device can be insertedat the various locations 28,30,32,34 to form a line of conduction blockthat prevents certain electrical signals from being sent from the focipoints 24. In necrotizing the cardiac tissue at several locations,thereby forming a line of conduction block in the pulmonary vein 36, thetransmission of aberrant signals believed to cause the arrhythmia can bereduced or in some cases altogether eliminated.

FIG. 2 is a partial cross-sectional view of the cryotreatment device 10of FIG. 1, showing the distal portion 38 of the device 10 in greaterdetail. In the exemplary embodiment of FIGS. 1-2, cryotreatment device10 comprises a multiple lumen catheter body 40 having an outer shaft 42configured to pierce and cool the cardiac tissue, and an inner shaft 44defining an inner lumen 46 in fluid communication with a cooling fluid.The outer shaft 42 of catheter body 40 may have a transversecross-sectional area that is substantially circular in shape, extendingfrom a proximal end (not shown) located outside of the patient's body toa transition region 48 on the catheter body 40. At transition region 48,catheter body 40 tapers distally to a needle-like ablation tip 50configured to pierce and contact cardiac tissue.

To cool the distal portion 38 of cryotreatment device 10 to asufficiently low temperature to induce necrosis when inserted intocardiac tissue, cryotreatment device 10 can be placed in fluidcommunication with a cooling fluid such as liquid nitrogen, nitrousoxide (N₂O), carbon dioxide (C₂O), chlorodifluoromethane,polydimethysiloxane, ethyl alcohol, chlorofluorocarbons (Freon), orother suitable fluid. The cooling fluid can be delivered in either aliquid or gas state through inner lumen 46, and injected into theannular space 52 between the outer and inner shafts 42,44 throughseveral apertures 54 disposed in the inner shaft 44. In one embodiment,for example, pressurized liquid nitrous oxide can be fluidly coupled tothe inner lumen 46 of catheter body 40, and ejected through severalapertures 54 disposed in the inner lumen 44. Using the Joule-Thompsoncooling effect, the apertures 54 are adapted to act as a throttlingelement (e.g. a throttling nozzle) for the cryogen, producingisenthalpic cooling as the fluid is expended from a relatively highpressure within the inner lumen 46 to a lower pressure as it enters theannular space 52. As the cryogenic fluid expands as it passes throughthe apertures 54, it transitions to a gas and impinges upon the interiorwall 56 of the outer shaft 42 cooling the distal portion 38 of thecatheter body 40. This temperature drop is then thermally transferredthrough the catheter body 40 and into the surrounding cardiac tissue 58,inducing necrosis at the target site 22. The cryogenic fluid issubsequently returned through annular lumen 52 to the proximal end ofthe device 10.

The number of apertures 54 can be varied to provide a desiredtemperature decrease to the distal portion 38 of the catheter body 40.The type of cryogen used and the pressure and/or volume at which thecryogen is delivered through the inner lumen 46 can also be selected toimpart a particular cooling characteristic to the device 10, as desired.In the exemplary embodiment of FIGS. 1-2, cryotreatment device 10includes several equidistantly spaced apertures 54 configured to provideuniform cooling through the distal portion 38 of the catheter body 40.It should be recognized, however, that the apertures 54 could be placedat any number of strategic locations, at either equidistant ornon-equidistant intervals, to direct the cryogenic fluid to a particularlocation within the device 10.

The outer and inner shafts 42, 44 of cryotreatment device 10 may befabricated from materials having certain desirable flexibility andthermodynamic properties. For example, the outer and inner shafts 42, 44may each be formed of a superelastic material such as nickel-titaniumalloy (Nitinol) to permit the cryotreatment device 10 to be insertedthrough relatively tortuous locations of the body without kinking Othersuitable biocompatible materials such stainless steel or a polymer/metalcomposition may also be utilized, depending on the particularapplication.

Referring now to FIG. 3, methods of using cryotreatment device 10 willnow be described in the context of a cryosurgical procedure to necrotizecardiac tissue 58 within a body lumen such as a pulmonary vein 36.Cryotreatment device 10 can be inserted through a previously positionedguide catheter 26 and advanced to a pre-mapped target site 22 within theheart believed to transmit aberrant electrical signals to one or morerelay points. As shown in FIG. 3, needle-like ablation tip 50 of device10 can be configured to pierce and contact the cardiac tissue 58 ofpulmonary vein 36, allowing the distal portion 38 of catheter body 40 tobe inserted into the cardiac tissue 58. A curved portion 60 on thecatheter body 40 may be adapted to orient the needle-like ablation tip50 in a direction substantially perpendicular to the tissue wall 58.

In one aspect of the present invention, cryotreatment device 10 can beconfigured to measure and control the transmural depth at which thedevice is inserted into the cardiac tissue 58. Controlled insertion ofthe needle-tip ablation tip 50 into the cardiac tissue 58 preventsdistension of the vein 36 from occurring, and prevents the ablation ofcardiac tissue not necessary to form the conduction block. Controlledinsertion of the needle-like ablation tip 50 into the cardiac tissue 58also ensures that the cryotreatment device 10 is inserted at asufficient depth to form the desired conduction block.

An ultrasonic probe 62 or other measurement device may be utilized tomeasure the precise depth at which cryotreatment device 10 is insertedinto the cardiac tissue 58. The ultrasonic probe 62 can be coupled tocatheter body 40 a predetermined distance from the needle-like ablationtip 50, and engaged to acoustically measure the depth at which thedistal portion 38 is inserted into the cardiac tissue 58. The ultrasonicprobe 62 may be coupled to the catheter body 40, or may be formed as aseparate element that can be advanced along the catheter body 40 andpositioned proximal the cardiac tissue 58. In one exemplary embodiment,the ultrasonic probe 62 may act as a guiding member for the device 10,eliminating the need for a separate guide catheter. Those of skill inthe art will readily recognize that other suitable devices for measuringthe insertion depth of the cryotreatment device 10 may be employed,including, for example, the use of an optical probe, acoustic reflectivecoatings, distal bipolar electrodes, or through the use radiographictechniques such as fluoroscopic marker bands.

In operation, a fluid controller or other similar device can be coupledto the proximal end of the cryotreatment device 10 and used to inject acontrolled flow of cryogenic fluid (e.g. liquid N₂O) through the innerlumen 46. One or more temperature sensors 39 on the distal portion 38 ofcatheter body 40 may also optionally be used to monitor the temperatureof the device 10 and adjust the flow rate via the fluid controller, asnecessary. An insulated sleeve 64 surrounding the catheter body 40 maybe utilized to thermally isolate the catheter body 40 proximal thedistal portion 38 to prevent ablating other areas of the body.

In certain embodiments, the cryotreatment device may include a couplingmember configured to couple multiple ablation tips together in an array.As shown in FIG. 4, for example, a coupling member 66 can be used toconnect multiple cryotreatment devices 10 together, forming a lineararray of needle-like ablation tips 50 that, when thermally cooled via acryogenic fluid, create a line of contiguous conduction block along thecardiac tissue 58 at the target site 22. The coupling member 66 can beconfigured to couple together any number of cryotreatment devicestogether in any desired array or pattern. The multiple cooling members10 applied in a sequential cooling method will allow the lesions to bemade in a stitched like fashion to ensure contiguous connection of allthe lesions. The method of stitching is accomplished by moving oneneedle 50 while the other needle 50′ is anchored and froze into thetissue. The sequence of operation would be as follows:

-   -   1. Insert two needles at start point and apply maximum freeze;    -   2. Thaw the proximal needle and reduce temperature on distal        needle;    -   3. Retract proximal needle and rotate around anchored distal        needle;    -   4. Apply maximum cooling on both needles and repeat steps 2-4.

FIG. 5 is a view of a cryotreatment device 68 in accordance with anotherexemplary 20 embodiment of the present invention. Cryotreatment 68comprises a catheter body 70 having several linearly disposed ablationtips 72 along a distal portion 74 that, when placed into fluidcommunication with a cryogenic cooling fluid, are configured to form aline of conduction block within a target site of the heart. Eachablation tip 72 may be configured similar to tip 50 described above,having a needle-like shape configured to pierce and contact the cardiactissue when inserted. The number of needles 72 and lumens 76 may be thesame as shown, or may be as few as two needles 72 for any number oflumens 76 in the method previously described. An inner lumen 76 in fluidcommunication with a source of pressurized cryogen at or near theproximal end of the device 70 is configured to cool each ablation tip 72in a manner similar that described above with respect to cryotreatmentdevice 10. The cryotreatment device 70 may also optionally include anultrasonic probe or other measurement means (not shown) for measuringthe precise depth at which the ablations tips 72 are transmurallyinserted into the cardiac tissue. An insulation layer 78 surrounding thecatheter body 70 thermally insulates the body 70 from ablating otherareas of the body.

To form a line of conduction block within a target site of the heart,ablation tips 72 can be aligned with a portion of the cardiac tissuebelieved to transfer the aberrant electrical signal(s) to one or moredownstream relay points, and inserted into the tissue at a controlleddepth. A pressurized cryogenic fluid can be delivered through thecatheter body 70, causing the ablation tips 72 on the distal portion 74to undergo a temperature drop to a temperature of about −40 to −100° C.,inducing necrosis in the surrounding cardiac tissue.

The destruction of more tissue than is necessary to form the conductionblock may be mitigated through the use of a series of smaller ablationtips. Moreover, the number, shape and arrangement of the ablation tipsmay be varied in accordance with the particular application. In certainapplications, for example, a cryotreatment device in accordance with thepresent invention may be configured to form a circumferential line ofconduction blocks at a target site within the heart.

In one exemplary embodiment shown in FIG. 6, a cryotreatment device 80in accordance with the present invention may include a catheter body 82having several needle-like ablation tips 84 on distal end 86 that, whenthermally cooled via a supplied source of cryogenic fluid, form acircumferential line of conduction block at a target site within theheart (e.g. about a pulmonary vein). Cryotreatment device 80 maycomprise an outer shaft 88, and an inner shaft 90 disposed within theouter shaft 88. The inner shaft 90 can be configured to deliver apressurized source of cryogenic fluid such as liquid nitrogen or N₂Othrough aperture 92 towards the interior surface 94 of distal end 86,causing the interior surface 94 of the distal end 86 of catheter body 82to cool and conduct heat.

Each of the needle-like ablation tips 84 can be configured to retractthrough several openings 96 disposed on the distal end 86 of thecatheter body 82. A control wire 98 extending proximally from eachablation tip 84 to a location outside of the patient's body may be usedto retract each tip 84 through its respective opening 96, allowing theoperator to adjust the precise depth at which the tip 84 is inserted thecardiac tissue. A flange 100 coupled to each ablation tip 84 preventsthe tip 84 from being pulled proximally through opening 96 as controlwire 98 is retracted. As with any of the other embodiments describedherein, an ultrasonic probe or other suitable device can be utilized tomeasure and, if necessary, control the penetration depth of the ablationtips 84 within the tissue.

In use, cryotreatment device 80 can be advanced to a target site withinthe heart, and, with the ablation tips 84 initially in a fully deployedposition, inserted into the cardiac tissue. Once the device 80 isinserted into the tissue, the operator can retract the control wire 98proximally a distance, causing the ablation tips 84 to retract fromwithin the tissue a slight distance (e.g. 0.5-3.0 cm). An ultrasonicprobe or other suitable device may be used to measure the precise depthat which the ablation tips 84 are inserted into the cardiac tissue. Atthe desired depth, a pressurized flow of cryogen is then deliveredthrough the device, causing the distal end 86 of the device, includingthe ablation tips 84, to cool to a temperature of about −40 to −100° C.,forming a circumferential line of conduction block within the body.

FIG. 7 is a partial cross-sectional view of a cryotreatment device 102in accordance with another exemplary embodiment of the presentinvention. Cryotreatment device 102 comprises an outer shaft 104 havinga proximal portion (not shown), a distal portion 106, and an inner lumen108 in fluid communication with a cooling fluid such as liquid N₂O. Thedistal portion 106 of cryotreatment device 102 may be enlarged slightly,orienting several retractable needle-like ablation tips 110 in a widerradial array, permitting the formation of a circumferential line ofconduction block at larger target sites. A control wire 112 operativelycoupled to each ablation tip 110 can be utilized to adjust thetransmural depth of the tip 110 into the cardiac tissue. A flangedportion 114 on each ablation tip 110 prevents the operator from pullingthe ablation tip 110 proximally through the tip openings 116 on thedistal portion 106 of the outer shaft 104.

Having thus described the several embodiments of the present invention,those of skill in the art will readily appreciate that other embodimentsmay be made and used which fall within the scope of the claims attachedhereto. Numerous advantages of the invention covered by this documenthave been set forth in the foregoing description. It will be understoodthat this disclosure is, in many respects, only illustrative. Changesmay be made in details, particularly in matters of shape, size andarrangement of parts without exceeding the scope of the invention.

1. A medical device for inducing controlled necrosis at a target sitewithin the body, comprising: an elongate member having a proximalportion, a distal portion, and at least one lumen therein providing acooling fluid path; a plurality of ablation tips in communication withsaid cooling fluid path near the distal portion of said elongated memberconfigured to contact and ablate tissue; and a control wire positionedin a defined distance from the plurality of ablation tips to control thetransmural depth of said plurality of ablation tips in to the tissue,wherein the ablation tip includes an inner shaft and an outer shaftaround the inner shaft, the inner shaft having a wall with openingsspaced along a longitudinal length of the inner shaft and positioned todirect coolant outward against the outer shaft.
 2. The medical device ofclaim 1, wherein the inner shaft defines an intake lumen for saidcooling fluid and the outer shaft defines an exhaust lumen for saidcooling fluid.
 3. The medical device of claim 2, wherein said innershaft includes at least one aperture configured to eject cooling fluidfrom said intake lumen into said exhaust lumen.
 4. The medical device ofclaim 3, wherein said at least one aperture comprises a throttlingelement.
 5. The medical device of claim 1, wherein the control wirecomprises a structure having a cross-section substantially larger than across-section of the ablation tip so as to impede insertion of theplurality of ablation tips beyond a defined point.
 6. The medical deviceof claim 1, further comprising an ultrasonic sensor mounted so as tomove toward the tissue as the ablation tip moves into the tissue.
 7. Themedical device of claim 1, further comprising a temperature sensorpositioned to monitor the temperature of the device at the target site.8. The medical device of claim 1, wherein the plurality of ablation tipsis retractable within the distal portion of the elongated member.
 9. Themedical device of claim 1, wherein the plurality of ablation tips islinearly arranged along the distal portion of said elongated member. 10.The medical device of claim 1, wherein the plurality of ablation tips isconfigured to form a line of conduction block at said target site. 11.The medical device of claim 1, wherein the distal portion of saidelongated member is radially enlarged.
 12. The medical device of claim1, further comprising a guiding member configured to transport saidelongated member to the target site.
 13. A medical device for inducingcontrolled necrosis at a target site within the body, comprising: anelongate member having a proximal portion, a distal portion, and atleast one lumen therein providing a cooling fluid path; a plurality ofablation tips in communication with said cooling fluid path near thedistal portion of said elongated member configured to form a line ofconduction block; and a control wire positioned in a defined distancefrom the plurality of ablation tips to control the transmural depth ofsaid plurality of ablation tips in to the tissue.
 14. The medical deviceof claim 13, wherein said elongated member includes an inner shaftdefining an intake lumen for said cooling fluid, and an outer shaftdefining an exhaust lumen for said cooling fluid.
 15. The medical deviceof claim 14, wherein the inner shaft includes a throttling elementconfigured to eject cooling fluid from said intake lumen into saidexhaust lumen.
 16. The medical device of claim 13, wherein the pluralityof ablation tips is linearly arranged along the distal portion of saidelongated member.
 17. The medical device of claim 16, wherein theplurality of ablation tips are arranged along a longitudinal axis of theelongate member.
 18. The medical device of claim 13, wherein the distalportion of said elongated member is radially enlarged.
 19. The medicaldevice of claim 13, further comprising a guiding member configured totransport said elongated member to the target site.
 20. The medicaldevice of claim 13, wherein the plurality of ablation tips areneedle-like ablation tips.